Dual circulation vapor generator



May 12, 1970 R. AL'LORENZINI ETAL 3,511,217

DUAL CIRCULATION VAPOR GENERATOR 4 Sheets-Sheet 2 Filed Sept. 18, 1968 5 5 m 2 rem M N o V qw a Q n A Y \wnwa nz A 2 B ATTORNEY R. A. LORENZINI ErAL 3,511,217

DUAL CIRCULATION VAPOR GENERATOR May 12, 1970 4 Sheets-Sheet 5 Filed Sept. 18, 1968 I 0R1IR5 70 24% 4 ATTORNEY y 1970 R. A. LORENZINI ErAL 3,511,217

DUAL CIRCULATION VAPOR GENERATOR Filed Sept. 18, 1968 4 Sheets-$heet L HENRY pfi/AL/PS ATTORNEY United States Patent O F U.S. Cl. 122-406 6 Claims ABSTRACT OF THE DISCLOSURE A dual circulation boiler having primary and secondary circuit wherein the secondary circuit is of the forced circulation type. Collection means are provided to receive the flow from the primary circuit and flow means are utilized to pass a portion of the flow from the collection means to the secondary circuit.

BACKGROUND It is known to provide a dual circulation boiler for the purpose of reducing blowdown wherein the boiler has two independent circulation sections, the primary or high duty section being in the radiant furnace portion of the boiler, the secondary section being disposed in a convection portion of the boiler. Each section is provided with its own independent circulating system, with the evaporation in the secondary section being approximately onethird of the total boiler output, or half that of the primary section. The primary section is provided with a steam drum which contains means for separation of the flow coming into the steam drum into a vapor phase and a liquid phase. Downcorners recirculate part of the liquid phase in the drum (about 70 percent) back to the inlet for the primary section, and tubes external to the boiler circulate the remainder of the liquid (about 30 percent of the total, or 40 percent of that recirculated in the primary section) to the secondary section. There is thus achieved a total steam production in the two sections equivalent to that of a conventional boiler having the same heat transfer and a 40 percent blowdown rate, at a much reduced overall blowdown rate.

In accordance with the present invention, it has now been discovered that the boiler water constituents (iron, copper, etc.) can be allowed to concentrate within the secondary section to a value higher than that normally allowed in the above unit by imposing forced circulation on the secondary section. The higher concentration of boiler water solids is permissible in the secondary section since the circulating pump allows the circulation ratio to be controlled at a relatively higher value. Sufficient velocity is maintained within the secondary tubes to reduce the internal tube deposition and corrosion. The higher concentration permitted within the secondary section thus allows a reduction in the blowdown rate.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and advantages thereof will become more apparent upon consideration of the following specification and accompanying drawings, in which:

FIG. 1 is a schematic vertical sectional view illustrating a vapor generator embodying the present invention;

FIG. 2 is a perspective view of the radiant portion of a boiler in accordance with another embodiment of the invention;

FIGS. 3 and 4 are enlarged section views of a water and steam drum of the vapor generator of FIG. 2 taken along lines 33 and 44 in accordance with the invention.

FIG. 5 is a perspective view showing details of the steam drum in accordance with the invention.

3,511,217 Patented May 12, 1970 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is illustrated a vapor generator, generally designated 12, comprising a setting 14 having a combustion chamber 16 defined (in part) by front wall 18, rear wall 20, side wall 22, and roof 24. In the roof is positioned a steam and water drum 26. Water wall tubes 27 are provided along the combustion chamber walls connected at the bottom with headers 28 and at the top either directly with the drum 26, or with headers 30 and riser tubes 32 leading to the drum. The lower headers 28 are fed in part through downcomers 34 leading from the steam drum 26.

The above is a description of the primary section of the vapor generator, in which the flow is by natural circulation. In operation, the flow is downwardly through the downcomers 34 to the headers 28, heat imparted to the wall tubes causing flow of the water and steam mixture upwardly to the steam drum.

The secondary section of the vapor generator comprises inlet headers 38, feeding division wall tubes 40, the latter leading to an upper header 42 connected to steam drum 26 via riser 44. However, the steam drum is divided into areas by bafiies in a manner to be described, and the riser 44 for the secondary section leads to a different area of the steam drum than the risers 32 and tubes 27 for the primary section.

Also, a separate downcomer 46 is provided leading from the secondary area or portion of the steam drum feeding the headers 38 for the secondary section. In this way, the secondary section is provided with a completely separate circulation system independent of that for the primary section. In the circulation system for the secondary section, a variable speed recirculation pump 48 forces water from the downcomer 46 through the division wall tubes by forced circulation.

In operation, in a manner to be described, a portion of the liquid in the primary area of the steam drum (for the primary section) is allowed to flow through a suita-bly sized orifice into the downcomer 46 for the secondary section, this portion constituting blowdown from the primary section.

Referring to FIG. 2, there is shown a perspective view of a slightly different type of boiler, which can be used to illustrate details in accordance with the invention. The secondary section here comprises portions 60 of side walls 62 of the radiant area of a natural circulation boiler. Riser tubes 64 lead from upper headers 66, for the side wall portions 60 to the center section 68 (designated secondary section) of steam drum 70. Downcomer 72 leads from the steam drum secondary or center section 68 back to lower headers 74 for the secondary section side walls 60, via recirculation pump 76.

The primary section of the boiler comprises the remaining walls 78 of the furnace, upper and lower headers 80 and 82, respectively, riser tubes 84, downcomers 86, and end primary sections 88 of the steam drum. Again, in operation, a portion of the liquid in the primary area of the steam drum is allowed to flow through orifices into the secondary section of the steam drum constituting blowdown from the primary section. Accordingly, the boiler of FIG. 2 is identical to that of FIG. 1 in principle except that diiferent water wall surfaces are utilized for the secondary wall section. In actuality, many arrangements of wall surfaces are possible Within the scope of the invention.

Details of the steam drum 70 are shown in FIGS. 3-5, and further details may be obtained from US. Pat. No. 2,675,888, granted to John Blizard, Robert A. Lorenzini, and Martin Frisch. The steam drum is divided longitudinally in the center by a baflle and end plates 102 into a semi-annular, center chamber 104 for the secondary flow. The center chamber itself is divided by plate 103 into a collection space 105 and a vapor and liquid space 107 wherein the two spaces are in communication through separators 108. The riser tubes 64 for the secondary section lead into the collection space 105 with the flow passing from the collection space through separators 108. From the separators, the liquid flows downwardly to the liquid level 110 of the area 107, and vapor passes outwardly through passageways 114 to be combined with steam in the primary chamber 106. In flowing through passages 114, the steam is washed by feedwater entering through flow line 116. Within center chamber 104, the feedwater flows between baffle 100 and a plate 117 parallel to the baflle. From the liquid level 110, the water flows into downcomer 72.

In the end chambers 106 of the steam drum for the primary section of the boiler, there is also provided a plurality of separators 118 at spaced locations along the drum in fluid communication with wall tubes 78 and the risers 84 (through collection chamber 119), so that a steam and water mixture flowing from the tubes and risers enters the separators. Steam flows from the separators into the vapor space 120 of the end (primary) chambers and liquid into the liquid space 122 thereof. At the top of the drum, a suitable drier 124 is disposed through which the steam flows to outlet tubes 126.

Referring again to FIG. 3, the bafile 100 in the portion adjacent downcomer 72 of the secondary section, partially encompassing the entrance to the downcomer, is provided with spaced orifices 132 disposed in the bafile so that a predetermined amount of water is permitted to flow from the liquid space 122 of the end (primary) chambers to the downcomer. Distribution pipes 134 in communication with line 116 extend longitudinally within the drum distributing feedwater into the liquid spaces 122 of the end (primary) chambers of the drum, as shown in FIG. 5. The flow from end sections 122 through orifice 132 to the secondary section downcomer 72 constitutes blow-down from the primary section.

In an example, in accordance with the invention, the flow in the secondary section of the boiler will amount to approximately one-third of the boiler output as in prior units. However, higher permissible levels in solids concentration in the secondary sections can be permitted through forced circulation within these sections. The reduced blowdown rate results in obvious economies in operation of the boiler. The higher velocities in the water wall and riser tubes effected by recirculation pump 76 reduce sludge and oxide deposits on these tubes. This is of particular importance in high pressure boilers.

As an additional advantage of the invention, apparent from FIG. 2, forced circulation permits the secondary section of the boiler to be located in a radiant section of the furnace, with high heat recovery.

Although the invention has been described with reference to a single boiler drum divided into chambers for the primary and secondary sections, an arrangement of two separate drums would be equally effective. Other drum internal arrangements are possible.

It is contemplated that the concepts of this invention would also be effective in connection with forced circulation in the primary section. In this case, there would be a blowdown flow from headers for the primary section controlled by suitably sized orifices.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What is claimed is:

1. A vapor generator comprising:

a boiler setting including walls defining a heating area;

a primary vapor generating section including vapor generating tubes lining at least a portion of the walls of the heating area;

a secondary vapor generating section including tubes exposed to the heating area;

collection means to receive the flow from the primary vapor generating section;

flow means to pass a portion of said flow from the collection means to said secondary vapor generating section, including orifice means to control the rate of flow;

said collection and orifice means being in an area of blowdown for said primary vapor generating section; and

forced circulation for said secondary vapor generating section.

2. A vapor generator comprising:

a boiler setting including walls defining a heating area;

a primary vapor generating section including first vapor generating tubes lining at least a portion of the walls of the heating area;

first inlet header means for said primary section;

a steam drum having first and second areas;

means communicating said first vapor generating tubes with the first area of the steam drum;

means in said first area to separate the fiow from the first vapor generating tubes into a vapor phase and a liquid phas a secondary vapor generating section within said setting including second vapor generating tubes exposed to said heating area;

second inlet header means for said second section;

means communicating said second vapor generating tubes with the second area of the steam drum;

means in said second area to separate the flow from said second vapor generating tubes into a vapor phase and a liquid phase;

first downcomer means adapted to transmit part of the liquid phase of the steam drum first area to the first inlet header means for said primary section;

orifice means to combine the remainder of the liquid phase of said first area with the liquid phase of the steam drum second area, said remainder constituting blowdown, from the primary vapor generating section;

second downcomer means adapted to receive the liquid phase of said steam drum second area;

forced circulations adapted to transmit said secondary area liquid phase to said second inlet header means;

and blow-off means adapted to remove solids from said secondary vapor generating section.

3. A vapor generator according to claim 2 wherein said secondary vapor generating tubes are in the radiation section of the vapor generator.

4. A vapor generator according to claim 2 wherein said blow-oif means is positioned upstream of the forced circulation means.

5. A vapor generator comprising:

a boiler setting including walls defining a heating area having a radiation section and a convection section;

a primary vapor generating section including first vapor generating tubes lining at least a portion of walls of the radiation section;

first inlet header means for said first vapor generating tubes;

an elongated steam drum including baflle means dividing the drum into first and second areas;

means communicating said first vapor generating tubes with said steam drum first area;

means in the steam drum first area to separate the flow from said first vapor generating tubes into a vapor phase and a liquid phase;

a plurality of first downcomers leading from the steam drum adapted to recirculate the liquid phase to said first inlet header means, the flow being by natural circulation;

a secondary section of vapor generating tubes defining additional cooling surface within the radiation section of the setting;

second inlet header means for said secondary section;

means communicating said second section of tubes with the steam drum second area;

second separation means in the steam drum second area to separate the flow into a vapor phase and a liquid phase;

second downcomer means to recirculate the second area liquid phase to said second inlet header means;

at least one orifice in said steam drum bafile means to transmit a portion of the liquid phase of the steam drum first area to be combined with the liquid phase of the second area, said orifice means being sized relative the first downcomers so that the flow through said orifice is approximately 40 percent of the flow recirculated in said first downcomers;

blow-01f means in said secondary section; and

forced circulation means in said second downcomer means downstream of said bloW-ofi means.

6. A vapor generator according to claim 5 wherein said steam drum bafile means divides the steam drum longitudinally into end first areas and a central second area, the orifices being in communication with each end area for flow therefrom;

References Cited UNITED STATES PATENTS 12/1958 Rehm l22406 12/1966 Rothemund et a1. 122-406 0 KENNETH W. SPRAGUE, Primary Examiner US. Cl. X.R. 

